CASE STUDY: Condition Monitoring for Transformers

Facing reliability issues, a long-term customer turns to Doble for help with its approach to transformer condition monitoring.

Customer Problem

A large independent power producer (IPP) based in Europe was dealing with demanding load cycles which were contemporaneous with a rise in transients on the system. These transients were considered to be possible sources of reliability issues, specifically with the bushings, where certain designs were considered suspect. In parallel, the IPP was also having problems with its existing online dissolved gas analysis (DGA) monitors. The IPP wanted to address the immediate issues, and also further develop its transformer condition monitoring program beyond data gathering at regular maintenance intervals.

Partnering with Doble

Doble has worked with this customer for over two decades, providing condition assessment services and failure investigations on its transformer fleet. To help address the current situation, the IPP worked with Doble on a bushing monitor pilot project. The doblePRIME IDD bushing monitor was installed on one transformer. During the successful pilot, an unmonitored bushing failed on an 800 MVA generator transformer. This bushing and subsequent transformer failure helped justify and reinforce the IPP’s need for proactive monitoring and response planning.

The IPP also decided to switch its reliability-plagued DGA monitors with the doblePRIME Delphi; this cost-effective device monitors Hydrogen, Carbon Monoxide, Acetylene, and Ethylene in a composite value. The company also installed doblePRIME DOMINO moisture in oil monitoring devices on some of the units.

NOTE: doblePRIME monitors can be used individually or as an integrated platform to track the health of transformers.

Result

After a successful pilot, the IPP installed doblePRIME monitoring platforms on four sets of single phase transformers, as well as its auxiliary transformers. The company is now in the process of outfitting its remaining fleet with doblePRIME platforms that will monitor DGA, moisture, bushing power factor and partial discharge (PD). Additionally, the IPP is integrating online data gathered through doblePRIME into the dobleARMS asset risk management system for better asset management decision-making capabilities.

Data from doblePRIME is already delivering timely results: PD in a GSU main tank was correlated with tap changer activity, so preventative maintenance was planned. Also, PD detected in a bushing on energization of the GSU was correlated with ramp up of the associated generator; the generator was then taken off-line for preventative maintenance.

In addition, Doble also performed PD surveys, which helped isolate a PD source seen at a turbine and at a GSU to the isophase bus. The issue, likely loose or cracked insulators, requires intervention on an appropriate timescale.

By looking at short-term concerns and long-term planning, the IPP has developed a comprehensive approach to transformer condition monitoring, one that has and will continue to find hidden problems before they turn into failures.